Luminescent panels



Nov. 8, 1960 A. MARzoccl-u ErAL 2,959,701

LUMINESCENT PANELS Filed lay 18. 1959 RESIN s- PHosPnoa) IN VEN TORS /hmfn Muzoec/l, Amun W/usoe 5mn/1v 64 HAM/sau C. dLAN/(wirft BY United States Patent O LUMINESCENT PANELS Alfred Marzocchi, Cumberland, and Alfred Winsor Brown, Woonsocket, RJ., and Harrison C. Blankmeyer, Wrentham, Mass., assignors to Owens-Corning Fiberglas Corporation, a corporation of Delaware Filed May 18, 1959, Ser. No. 813,890

15 Claims. `(Cl. 313-108) This invention relates to luminescent panels, and is particularly directed to means to increase the intensity of emitted light per unit of panel area.

At the present time luminescent panels are known which comprise: (l) fluorescent devices in which a light responsive phosphor is energized by ultraviolet or visible light and which emits its visible radiation over a prolonged period of time; (2) electroluminescent devices in which an alternating or pulsating electric field activates a field-responsive phosphor, and (3) luminescent devices in which a phosphor is activated by radiation from a decaying radioactive source intimately mixed therewith. In each of the known devices, the active layer of the phosphor is made relatively thin, because there is no way in which light originating deep in the mass can be transmitted to the surface except obliquely between phosphor particles or by retlection; and, further, in the case of phosphors excited from an alternating field or from an external radiation source, the activity of the phosphor increases as the thickness of the phosphor-containing layer of the panel decreases. Thin panels, however, have low light outputs per unit of area unless the applied power is inordinately high.

The present invention has for its primary object to increase the light output per unit of area of a phosphorcontaining panel regardless of the method of excitation of the phosphor. Broadly defined, the invention comprises introducing into the phosphor bearing layer a great multiplicity of glass fibers or flakes so oriented as to collect light emitted by the phosphor particles within the layer and to conduct such collected light to the surface of the layer for emission to the outside thereof.

The following specification explains in detail an embodiment of the invention in conjunction with each of the previously defined methods of phosphor excitation, and the accompanying drawings show diagrammatically light emitting panels constructed in accordance with the invention.

In the drawings:

Figure 1 is a diagrammatic elevational view of a sheet of plastic material containing a phosphor and particulate glass elements oriented generally parallel to a major axis of the sheet;

Fig. 2 is a diagrammatic elevation view of sections of the sheet of Fig. 1 cut apart;

Fig. 3 is a diagrammatic elevational view of a sheety of plastic material constructed by recombining the sections shown in Fig. 2;

Fig. 4 is a diagrammatic elevational view of an apparatus suitable for imparting parallel orientation of particulate glass elements;

Fig. 5 is a diagrammatic sectional view of a mold operatively associated with the apparatus and elements of Fig. 4;

Fig. 6 is a sectional view of a luminescent panel element constructed by the apparatus of Figs. 4 and 5;

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Figures 1 to 3 of the drawings show steps in the con- I struction of a luminescent panel of the type in which radiation such as ultraviolet or visible light activates the phosphor. The phosphor material may comprise any of the known phosphors such as metallic sulfides of which zinc sulfide is most commonly used. The phosphor may be dispersed throughout a suitable ,transparent plastic mass. Suitable transparent plastics for this purpose may for instance, be methyl methacrylate and other acrylics,

Fig. 7 is a diagrammatic sectional view of a luminescent 70 panel element embodying one form of the invention;

regenerated cellulose, cellulose esters and ethers, various epoxies and numerous polyesters.

In addition to acting as a carrier for the phosphor material, the resinous mass also contains a great multiplicity of generally oriented glass fibers or flakes which are designated G in the drawings. In general it is preferred that glass fibers in the order of 1 mil diameter and glass flake in the order of l mil thickness be used. However, thinner sections of glass are operable, so long as they have a minimum thickness several times the wave-length of the longest visible radiation to be collected and transmitted.

The glass fibers or flakes G may be introduced into the plastic material in any suitable manner and may comprise as much as percent by weight of the phosphorcontaining plastic mass. The orientation of the particulate glass flakes or the fibers is generally perpendicular to the plane of the face of the panel constructed there from. v

One manner of constructing a panel is to form a plate or sheet of the phosphor-containing and glass bearing resin with the glass oriented horizontally as indicated in Fig. 1. This can be accomplished by machines that are well known in the art in which the plastic material is rolled between belts or rollers and the glass material introduced during the formation of the sheet. Similar techniques are used, for example, in the manufacture of glass reinforced fishing rods and the like.

Once the horizontally oriented ber or flakes are contained in the phosphor bearing resin sheet, the sheet may be sliced into lengths, with one dimension of each slice representing the ultimate thickness of the desired panel. For example, if a 1" thick panel is desired, then the slicing of the sheet carrying the horizontally'oriented glass will take place at each inch of its length, to form sections or strips of the material as shown in Fig. 2. By rotating the strips so formed the orientation of the glass is changed from a horizontal to a vertical direction as indicated in Fig. 3. The slices or strips may then be adhered together to form an integral panel or body with each area thereof carrying the fibers or llakes'properly oriented.

It has been found that the fine glass fibers or thin flakes act as light gathering elements within the phosphor-containing plastic and that they possess the property of transmitting gathered light along their lengths so that the light is emitted from the surface of the panel. In this respect, then, the fibers or Hakes act as collecting pipes for the internally originating light in the panel, with the light being given off at the end of the pipe, or at the surface of the panel.

To increase the acceptance of the light within the panel it is desirable, in some instances, to coat the glass of the reflection-reducing Huoride coating, the glass par-` ticles in the Hake form can readily be oriented to reflect light received within the phosphor containing resin sheet to the exterior thereof. Such an orientation can be accomplished by mechanically deforming the sheet during cure, or by curing the sheet on a mold with projections set at the proper angle for maximum reflectance. 'Ihe glass flakes thus act as reflecting planes close to the surface of the sheet, and light emitted from a phosphor particle placed either deep within the resin or on the surface of the flake will be reflected to the outside of the panel.

A panel of the type shown in Fig. 3 is admirably suited for activation by ultraviolet or visible radiation since it is a structurally integral unit with both of its sides exposed. If the panels are used, for example, as roofing material for buildings the panels will be exposed to radiation from the sun on their upper surfaces and will store the energy derived from such radiation during the day and will give olf light from the activated phosphors during the night. Such roofing materials may be of definite advantage in warehouses, for example, or in other buildings where a subdued night light source is all that is required.

It will be seen that the panels are essentially translucent to visible light during the day and can thus act as skylights. However, it will also be seen that there is some luminescent effect present even during the day by reason of the action of the panel in changing the ultraviolet radiation received on its uppersurface to visible light emitted from its lower surface. Thus the panel will give off more light in the visible spectrum than would a panel of the same material not containing any activatable phosphor.

Figures 4 to 7 of the drawings show electroluminescent panels constructed in accordance with the invention and containing the aforementioned vertically oriented glass fibers or Hakes. Panels of this type contain a field responsive phosphor and small quantities of electroconductive material such as copper sulfide to increase the activity of the panel, all embedded in a transparent dielectric resinous film. The layer of phosphor bearing film is, as previously mentioned, usually made thin to reduce the power required for activation. By providing an efficient means for transmitting light through the phosphor bearing layer, the present invention makes it possible to use a sandwich construction in which a number of superimposed but separately activated phosphor-containing layers are employed.

Such a sandwich construction is shown, somewhat diagrammatically, in Figure 8, and the steps involved in preparing the several layers of the active sheets are shown in Figures 4 to 7.

The desired orientation of the fibers or flakes of glass can be accomplished in various ways, as by charging a plate P to a relatively high voltage and attracting the glass thereto electrostatically. Some types of glass that are used commercially for fibers and Hakes require an acid preparation before they are capable of accepting an electrostatic charge. The charged fibers or Hakes thus depend vertically from the surface of the plate P as indicated in Figure 4 and will lie parallel to each other. The charged plate with the glass particles electrostatically adhered thereto can be lowered into a mold M containing a mass of uncured liquid phosphor bearing plastic material, without disturbing the orientationA body of cured resinous material containing a mass of dispersed luminescent particles and a mass of light collecting and conducting glass fibers or Hakes randomly dispersed -throughout and extending, for the most part, completely through the resin sheet from its bottom to its top planar surfaces. However, some of the glass particles preferably have a length shorter than the thick ness of the sheet so that they terminate at one end on a surface of the sheet and at the other end within the sheet, as indicated in the magnified view, Fig. 6.

The preparation of the sheet by the electrostatic attraction of the glass fibers or flakes to the plane surface of the plate P prior to introduction into the plastic is particularly advantageous for panels wherein a light activatable phosphor is used in conjunction with fibers or Hakes made of quartz. As is well known, quartz is transparent to and conducts ultra-violet light so that a panel containing a phosphor activatable by radiation in the ultraviolet range can be energized from a rather concentrated source of ultraviolet light shining on the surface at which all of the fibers or flakes terminate. The ultraviolet radiation from the source will be conducted deep into the mass of the panel by the quartz particles and can thus activate phosphor particles that would otherwise remain inert due to the opacity of the phosphor particles themselves and of the resin to the activatng radiation. Light from the activated phosphors will be conducted to the opposite face of the panel either by direct radiation where the phosphors have a direct light transmitting path or by transmission into and collection by those of the fibers or flakes that extend to the emitting face. Such a panel, when used as a ceiling of a room, for example, can be activated by a mercury vapor arc or other ultraviolet source behind it and will emit a diffused light in the visible range over-the entire exposed ceiling surface, giving a more general illumination to the room than would be obtained from the concentrated source.

The vertical orientation of the fibers or Hakes in the plastic mass can also be accomplished by casting a thin film of the phosphor and flake bearing resin on a flat surface and over a frame of thin, parallel wires. While the resin is still uncured the wire frame can be withdrawn vertically through the sheet and the flow caused by the passage of the wires will impart a vertical orientation to the fiber or flake particles in the resin.

Another method of achieving vertical orientation of the fibers or flakes with respect to the plane of the phosphor bearing resin sheet is to impregnate a glass pile fabric with the uncured resin and subsequently cure the impregnated mass. Glass textiles are woven into fabrics of the velvet type which have a rather deep and dense pile extending upwardly from the warp and woof threads 0f the backing. The phosphor bearing resin can be cast over the pile fabric, cured, and the warp and wo'of threads of the backing removed. The resulting sheet can be cut to the desired thickness and the threads that formerly constituted the pile of the velvet fabric will be embedded in the sheet and will extend in a direction generally normal to the major plane thereof which will ultimately constitute the light emitting surface of the panel or sheet.

To construct electroluminescent panels, the glass and phosphor bearing resin sheet 10 is then covered on each of its top and bottom planar surfaces with a layer or film 11 of electrically conductive light dispersing glass particles which again, may be either fibers or Hakes. This film 11 preferably comprises thin, continuous layers of horizontally oriented glass Hakes which have previously been leached or frosted to make them light dispersive and subsequently coated with a thin transparent oxide coating which will render them electrically conductive. Such conductive coatings are well known in the art. Alternatively, however, the thin frosted light dispersing Hakes can first be laid on and adhered to the plastic sheet and subse quently made electroconductive by the application of a coating of, for example, tin oxide.

There is thus provided a thin sheet of phosphor and glass bearing resinous material which may be made very thin and flexible, for example, IAB" thick, covered on each side with a thin electrically conductive light dispersing lm or layer of glass particles. When such a sheet is stressed electrically to the proper voltage by an alternating or pulsating current the phosphor particles glow within the resin mass and light emanating therefrom is collected by the glass bers or flakesand conducted to the surface of the sheet, although some of the light from particles close to the surface will pass directly to the surface in the usual manner. Light striking the thin electrically conductive transparent layer of glass flakes 11 is dispersed to give a uniform glow over the entire sheet so that rays of light emanating from the ends of the bers or flakes are not sharply conned after they have passed through the light dispersing lms or layers.

As indicated in Fig. 8 a number of sheets so prepared can be physically associated in a sandwich construction comprising a plurality of contacting superimposed layers.

As there shown alternate ones of the coating lms, designated 11A are connected to one side of a source of high stressing potential 12 and the remaining alternateconductive lms designated 11B are connected to the opposite side of the energizing source, which may be either an alternating or pulsating current source.

Light originating in the .uppermost layer of the sandwich construction is conducted to the surface thereof and is dispersed by the adjacent layer of horizontally oriented conductive light dispersing glass particles 11B. It is thence passed into the next succeeding layer, through this layer and ultimately is emitted from the surface of the sandwich which is indicated at 13 in Fig. 8. Thus, strict alignment of the light conducting bers or akes in the,I

Glasses," by Woldemar A. Weyl, published by The Society of Glass Technology, Sheeld, England, in 1951. Thus the characteristic fluorescence or luminescence of the phosphor-containing glass particles may be added to the characteristic fluorescence or luminescence of the phosphors contained in the plastic mass or, the fluorescence or luminescence of thev phosphor-containing glass itself may be relied upon for the illumination of the lm or layer.

Leaching the ber or flake particles prior to incorporation in the construction of the present invention not only alters the light dispersing qualities of the glass elements but may also be used to provide spatial irregularities on the ber or flake particles for the reception of phosphor materials prior to incorporation in the plastic mass. In this manner, the sources of luminescence are brought into very close contact with the light collecting and conducting bers or flakes. The phosphor particles carried by the glass may be, of course, in addition to the phosphor particles carried by or incorporated in the resin.

The ber or ake may also be coated with a radioactive substance which will cause luminescence of a phosphor carried within the resin mass. A lm or sheet made luminescent by this expedient is shown in Fig. 9. As there diagrammatically indicated the ber or ake glass particles are oriented vertically with respect to the plane of the sheet and are previously coated with a radioactive material such as atomic pile wastes, naturally occurring materials such as radium, synthetically produced materials such as radioactive barium or sodium isotopes or,

when the -glass particles are flakes, a radioactive gas such as tritium or promethium. The phosphor particles are carried in and dispersed throughout the resin mass. The resin mass is protected on each of its two exposed surfaces by a shielding layer 14 which will prevent the emission of the radioactivity from the activating materials incorporated within the resin body. This layer of shielding glass may be made from, for example, high lead glass flake and its thickness will be dictated by the degree of radioactivity exhibited by the material within the lm or sheet. In this construction, the phosphor particles are activated by the emission from the radioactive material carried by the fiber or ake and the light therefrom is again collected by the vertically oriented glass elements and is conducted to the surface of the sheet to be emitted through the shielding layer of glass flake or bers. A panel constructed with a sheet or film of this material will be selfilluminating in that it does not require any external light or alternating eld for activation of the phosphor particles. Further, if desired, the back of the panel or sheet can be metallized to provide a mirror-like surface which will reflect, through the light pipes formed by the embedded ber or flake, light which would otherwise be emitted from the rear surface of the panel or sheet.

As above stated, the radioactive material may comprise an activating agent such as tritium adsorbed as a gas on the surface of the glass. This adsorption may be accomplished by heating the glass flake to a temperature in the order of 400 or 500 F. to drive 0E water and other volatile contaminants. When cooled, the glass is cleaned and will adsorb the tritium which canA be bled into the mass of glass in the form of heavy water or as the gas. This results in a glass flake that is radioactive and will activate the phosphor so long as the emission continues from the radioactive material at a suitable level.

'Ihe radioactive material used to activate the phosphor may be incorporated in the plastic material in other ways. For example, the radioactive material may be adsorbed on particles of silica gel which will comprise a network of transparent molecules. The silica gel can be mixed directly into the resin mass or can be adhered to the surface of the glass ber or flake.

If a leached glass ber or ake is used and made radioactive as above described, the irregular surface thereof may be used also to hold at least some of the phosphor particles which are activatedby the radioactive material. 'Ihe treated glass ber thus incorporates not only the radioactive source but also the phosphor prior to its incorporation in the resin. Here again, additional phosphor may be mixed into the resin if desired.

The glass itself may be made radioactive and may thus comprise not only light conductors as above described, but also an activating source for the phosphors carried by the glass elements or incorporated in the resin matrix. Uranium glasses, for example, are well known a'nd if made from the oxide of U238 slightly enriched with U235 will act in the desired manner to activate the phosphor particles to produce a visible light which will be collected and conveyed to the surface of the sheet in the same manner as if the radioactive source were obtained by treatment of the fibers or flakes as above described.

It will be seen that the invention provides a luminescent panel which is luminescent in depth, in that the light emanating from phosphor particles deep within the mass is conducted to the surface of the lm or sheet by the light conducting glass fiber or flakes. In contrast, known luminescent panels are made very thin and are, in general, only surface active since the phosphors themselves are opaque and will cut off light originating in particles behind them. By the addition of the light accepting and conducting bers or flakes the present invention makes it possible to greatly increase the depth of the panel and thus the intensity of light emitted therefrom per unit of surface area. The intensity of emitted light per square foot of panel area can be further increased by increasing the exposed surface of the panel as by corrugating the surface as disclosed in Fig. 10. As there indicated, the exposed light-emitting surface of the panel is formed with a series of longitudinally extending grooves 20. Such grooves may be readily molded or otherwise formed either during the original casting of the resin or subsey quently, or the glass bearing resin sheet may be corrugated in its entirety so that both the upper and lower surfaces are grooved or prismatic. 'I'he prismatic surface thus formed'results in a greatly increased light emission for each square foot of panel; the area of the light emitting surface being greater than the projected area of the panel. As is the case of the panels having plane surfaces as above described, the prismatic or contoured panel is luminescent in depth by reason of the light collecting properties of the properly oriented glass fibers or flakes.

What we claim is:

1. A luminescent panel comprising a sheet of plastic material, a great multiplicity of elongated transparent glass elements embedded -in said plastic material with their longer axes generally oriented in a direction normal to a light-emitting surface of said sheet, and an activatable phosphor dispersed throughout said plastic material, at least some of said glass elements extending to the surface of said sheet whereby light emanating from subsurface phosphor particles within the mass of said sheet is collected in and conducted by said glass elements to the surface of said sheet and emitted therefrom.

2. A luminescent panel as defined in claim 1 in which said phosphor is field responsive.

3. A luminescent panel as defined in claim l in which said phosphor is light responsive.

4. A luminescent panel as defined in claim l in which said phosphor is activated by radioactive radiation, and said sheet contains a radioactive source.

5. A luminescent panel as defined in claim 4, and protective transparent coatings on the exposed surfaces of said sheet to absorb radioactive emissions which would otherwise escape from said surfaces.

6. A luminescent panel as defined in claim 1 in which the activatable phosphor is contained at least in part within said glass elements.

7. A luminescent panel as defined in claim 1 in which said glass elements are quartz glass and said phosphor is activatable by ultraviolet radiation conducted into said sheet by said glass elements.

8. A luminescent panel as defined in claim 1 in `which at least a part of said phosphor is collected on the surfaces of said glass elements in said plastic mass.

9. A luminescent panel as defined in claim 1 in which the surfaces of said glass elements are reduced in reflectivity by a fluoride coating thereon.

10. A luminescent panel in accordance with claim 1 in which the area of the light emitting surface is greater than the projected area of the panel.

l1. A luminescent panel in accordance with claim 10 in which the light emitting surface is at least in part prismatic.

12. A luminescent panel comprising a sheet of plastic material, a great multiplicity of elongated transparent glass elements embedded in said plastic material and generally oriented in a direction normal to a light emitting surface of said sheet, a field responsive phosphor dispersed throughout said plastic material, at least some of said glass elements extending to the surface of said sheet whereby light originating in a phosphor particle deep within the mass of said sheet is collected in and conducted by said glass elements to the surface of said sheet and emitted therefrom, and electroconducting means in contact with opposite maior faces of said sheet, at least one of saidelectroconducting means comprising a film of transparent electroconducting .glass particles.

13. A luminescent panel as defined in claim l2 in which each of said electroconducting means comprises a film of transparent electroconducting glass particles.

14..A luminescent panel as defined in claim 12 in which said glass particles in said film are light diffusing with respect to light emitted from said surface of said sheet.

15. A luminescent panel comprising a plurality of contacting superimposed layers, each layer comprising a sheet of plastic material, a great multiplicity of elongated transparent glass elements embedded in said plastic material and generally oriented in a direction normal to a light emitting surface of said sheet, a field responsive phosphor dispersed throughout said plastic material, at least some of said glass elements extending to the surface of said sheet whereby light emanating from subsurface phosphor particles within the mass of said sheet is collected in and conducted by said glass elements to the surface of said sheet and emitted therefrom, and electroconducting means in contact with opposite major faces of said sheet, each of said. electroconducting means comprising a film of transparent electroconducting glass particles, and means to impose an energizing voltage difference across each of the sheets of the panel.

References Cited in the file of this patent UNITED STATES PATENTS Re. 24,540 Michlin -Q Sept. 23, 1958 2,091,152 Malpica Aug. 24, 1937 2,689,188 Hushley Sept. 14, 1954 2,857,541 Etzel et a1 Oct. 2l, 1958 

1. A LUMINESCENT PANEL COMPRISING A SHEET OF PLASTIC MATERIAL, A GREAT MULTIPLICITY OF ELONGATED TRANSPARENT GLASS ELEMENTS EMBEDDED IN SAID PLASTIC MATERIAL WITH THEIR LONGER AXES GENERALLY ORIENTED IN A DIRECTION NORMAL TO A LIGHT-EMITTING SURFACE OF SAID SHEET, AND AN ACTIVATABLE PHOSPHOR DISPERSED THROUGHOUT SAID PLASTIC MATE- 